An ultrasound diagnostic apparatus is an apparatus which forms an ultrasound image based on reception data obtained by transmitting and receiving ultrasound, and displays the formed ultrasound image. In general, the ultrasound diagnostic apparatus has a plurality of operation modes (such as a B mode, a Doppler mode, etc.). Further, there is known an ultrasound diagnostic apparatus which has a plurality of measurement functions. An example of such a measurement function is a function of blood vessel measurement, and, for example, an IMT measurement of ultrasound is a representative example of blood vessel measurement.
The IMT measurement is a measurement targeted to a blood vessel such as, for example, a carotid artery, and is targeted to an Intima-Media Thickness of a blood vessel wall. The blood vessel wall has a three-layer structure including an intima, a media, and an adventitia, viewed in that order from the side of a bloodstream. In the IMT measurement, a thickness of a combined structure of the intima and the media (intima-media thickness, or IMT) is measured.
For example, Patent Document 1 discloses an invention related to the IMT measurement by an ultrasound diagnostic apparatus. Specifically, Patent Document 1 discloses an invention in which a region of interest including a blood vessel in an ultrasound image is divided into three regions including an inner cavity region of the blood vessel, an intima-media region, and an adventitia region by an inner cavity side dividing line and an adventitia side dividing line; an inner cavity side boundary is extracted in a range limited to the inner cavity side from the inner cavity side dividing line; an adventitia side boundary is extracted in a range limited to the adventitia side from the adventitia side dividing line; and the intima-media thickness is measured based on a distance between the inner cavity side boundary and the adventitia side boundary.